1. Technical Field
The invention relates to a heat-insulated conduit having at least one internal tube, a heat-insulating layer based on polyurethane foam and surrounding the internal tube, a film surrounding the heat-insulating layer and a corrugated external tube made of thermoplastic.
2. Description of the Background Art
EP 0 897 788 B1 discloses a heat-insulated conduit for use in local and district heating systems, as drinking-water and wastewater conduits, and in numerous other special sectors, which conduit is made up of an internal tube carrying the medium and made of plastic, preferably cross-linked polyethylene; a heat-insulating layer based on polyurethane foam and surrounding the internal tube; and an external jacket made of plastic and equipped with a corrugation. A film made of plastic is additionally provided between the heat-insulating layer and the external jacket.
The known conduit is easy to bend, and can be delivered directly to the construction site coiled into rings or onto drums. Because it is easy to bend, the conduit can be adapted without difficulty to almost all terrain conditions during installation.
With the known conduit, which is available on the market under the brand name “Calpex,” the heat-insulating layer is made of hard polyurethane foam, which imparts outstanding heat-insulating properties to the conduit. A disadvantage of this conduit is that the bending radius is relatively large and is limited, for example in the case of the smallest type of tubing, to 0.7 m.